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The T249 Vigilante was an attempt at an advanced mobile anti-air system in the 1950s, consisting of a motorized terrain chassis (made from a modified M113 APC), fitted with the T250 cannon. It was a huge, six barreled Gatling cannon, the largest Gatling gun ever built, using a 37x219mmSR cannon shell, and driven by a hydraulic system, allowing for a variable rate of fire between 150rpm, and 3000rpm.
The Vigilante project was abandoned around 1960, as it was found that Surface to Air Missiles were a far more practical approach for taking down enemy jet planes. Presumably part of it was the setup being built for a 192rd drum of linked cannon shells, which would last all of 5 seconds at max RPM, a somewhat narrow margin. Presumably a larger drum fitting a longer belt could be made (though crew would have to be able to handle and load it as well), and likely multiple of these guns would have been used in one defensive position, also not necessarily at the highest RPM.